Often permanent magnet motors used in automotive application require the use of more than one speed, usually a lower speed for general purpose operation and a maximum speed for worst-case operation. Multiple speed operation of a cooling system module of a vehicle provides a more optimized engine temperature and operation, which consequently contributes to improved fuel economy.
For permanent magnet direct current brush motors (PMDCBM), historically lower speeds (multiple speed operation) have been achieved by the following methods: Adding a resistor in series with the motor; Switching out brushes; Dual-armature winding with dual-commutator; Adding an additional third brush (short out coils); External or internal electronic control comprised of but not limited to SSR, (Solid State Relays); Linear control; and PWM, (Pulse Width Modulation).
With reference to FIG. 1, a conventional electric motor, generally indicated at 10, is shown having a dual-armature winding and dual-commutator configuration. Thus a first winding 12 is associated with a first commutator 14, and a second winding 16 is associated with a second commutator 18. The configuration of DC motors having dual-armature winding and dual-commutator are well known in the art. The following US. Patents describe the art of dual-armature winding and dual-commutator: U.S. Pat. Nos. 5,925,999 and 4,910,790, the content of each patent is hereby incorporated into the present specification by reference.
An electric motor with dual-armature winding and dual-commutator configuration provides an integrated solution for two speed application. Since there are no external components required for a second speed of operation, these types of motors are very commonly used in automotive applications. Furthermore, the motor efficiency is significantly better during the low speed operation with this solution than adding a series resistor. Compared to series resistor solution/method for low speed, beside the conventional motor losses, there is an additional loss of energy. This additional energy loss is dependent of the resistance of the resistor in series with the motor and the operating current (this energy loss is equivalent to I2*R).
The conventional motor shown in FIG. 1 was a high selling product in engine cooling for automotive applications, but with the development of more cost effective and reliable resistors, this product lost market share.
Thus, there is a need to improve the configuration of a dual-armature winding and dual-commutator motor by reducing the material and component usage and the overall system cost so this type of motor will again become an attractive and competitive product for engine cooling applications.